Thermal Management of Military Power Supplies: Liquid Cooling & Export Power

Powering Next-Generation Military Vehicles: Why Cooling Architecture Matters More Than Ever

Modern military vehicles are evolving rapidly, bringing higher power demands, hybrid-electric architectures, and new expectations for reliability and performance. One of the most significant shifts is the move toward vehicle “export power”, where onboard energy systems supply power to external equipment such as radar, communications, and mission systems.

But with this shift comes a challenge: traditional power conversion designs are no longer sufficient.

To meet the demands of next-generation platforms, engineers must rethink not just power conversion, but how these systems are cooled, protected, and integrated.

Key Takeaway:
Next-generation military power systems require high-voltage architectures and advanced thermal management. Liquid cooling—especially modular and immersion-based approaches—enables higher power density, improved reliability, and better performance in harsh environments. 

The Shift to High-Voltage Export Power

Historically, deployable military systems have relied on 120/240 VAC or 28 VDC power generated by vehicle alternators or portable generators, typically supporting power levels between 10 kW and 30 kW. While these systems have been effective, they introduce several operational challenges, including high audible noise, increased thermal signatures, elevated fuel consumption, and the need for heavy cabling due to high current levels. For example, delivering more than 10 kW at 28 VDC can require currents exceeding 500A, which leads to large and expensive conductors, complex overload protection systems, and reduced overall efficiency.

Next-generation military vehicles are addressing these limitations by transitioning to high-voltage energy storage systems, typically operating around 300 VDC. These systems utilize advanced technologies such as lithium-ion batteries, nickel-metal hydride (NiMH) batteries, and supercapacitors. By increasing system voltage, these platforms achieve a dramatic reduction in current, often by as much as 90% (for example, reducing current from 500A to approximately 50A). This shift enables the use of smaller conductors, reduces system losses, improves power density, and allows for more compact and efficient power conversion systems.

Comparison: Legacy vs. High-Voltage Export Power

The Real Challenge: Harsh Military Environments

Export power converters used in military vehicles must operate reliably in some of the most extreme conditions imaginable. These systems are required to withstand wide temperature ranges, from –46°C (–51°F) to +54°C (129°F), while enduring significant mechanical stress, including shock and vibration in accordance with MIL-STD-810 standards. In addition, they are frequently exposed to harsh environmental elements such as dust, moisture, and even full immersion, all while operating in remote locations where maintenance access is limited. Given their role in mission-critical applications, reliability is not just important; it is essential.

In many cases, these converters are mounted externally on the vehicle, often below the fording line, leaving them fully exposed to environmental hazards. At the same time, vehicle manufacturers are pushing for increasingly higher power densities, typically ranging from approximately 3.4 W/in³ to over 10 W/in³. These competing demands,  extreme durability, and higher power density place significant pressure on thermal design and cooling strategies.

Cooling Strategy: The Critical Design Decision

Thermal management has become one of the most important factors in the design of modern power conversion systems. The choice of cooling architecture directly impacts several key aspects of system performance, including:

• Reliability – Component temperatures directly influence lifespan and failure rates
• Size and weight – Cooling method affects overall system footprint and integration
• Maintainability – Moving parts and accessibility impact service requirements
• Cost – Both upfront design complexity and long-term operational costs

Selecting the right approach is critical to ensuring long-term performance in demanding military environments.

One of the most straightforward approaches is forced air cooling. Direct air cooling uses internal fans to move air across electronic components and can achieve relatively high power density. However, in harsh environments, this approach presents serious risks:

• Dust and debris can accumulate on internal components
• Moisture can combine with contaminants to create conductive buildup
• Increased risk of electrical failure over time
• Not suitable for sealed or externally mounted systems

As a result, direct air cooling is generally not recommended for environmentally exposed military applications.

An alternative is indirect air cooling, often referred to as a “wind tunnel” design. In this configuration, air is used to cool heat sinks while the electronic components remain isolated from the external environment. While this provides better protection, it introduces several trade-offs:

• Larger system size due to airflow channeling
• Continued reliance on fans as a wear-out component
• Not compatible with immersion or fully sealed designs
• Limited scalability across multiple platforms

Ultimately, air-cooled solutions, whether direct or indirect, struggle to meet the demands of harsh military environments.

Liquid cooling provides a more robust foundation for these applications by enabling:

• Fully sealed enclosures that protect electronics from environmental exposure
• Significantly higher heat transfer efficiency compared to air
• Greater flexibility in system design and thermal management
• Improved performance in high-power, high-density applications

The most common liquid cooling method is cold plate cooling. In this approach, heat-generating components are mounted directly to a flat plate through which coolant, typically water or a water/glycol mixture, circulates to remove heat. This method is proven and effective, particularly for sealed systems, and offers several advantages:

• Reliable and widely adopted cooling approach
• Effective heat removal for high-power components
• Compatibility with sealed, ruggedized designs

However, it is not without limitations:

• Complex mechanical design and integration
• Larger physical footprint in some configurations
• Thermal bottlenecks for components not directly mounted to the plate
• Increased internal wiring, which can reduce overall reliability

Cooling Approaches Comparison

The Hidden Problem: Internal Temperature Rise

Even with liquid cooling, a critical challenge remains, internal temperature rise within the power conversion system. In many designs, internal air temperatures can exceed the coolant temperature by 40°C or more. For example, with a coolant temperature of 80°C (176°F), internal air temperatures can rise to 120°C (248°F) or higher.

This creates serious reliability concerns, particularly for components that are not directly coupled to the cooling surface. Integrated circuits, which may only dissipate small amounts of power, are highly sensitive to ambient temperature and rely on surrounding air for heat dissipation. Likewise, passive components can experience significantly reduced lifespans when operating above approximately 100°C (212°F). As a result, even if high-power components are effectively cooled, the overall system reliability can still be compromised by elevated internal temperatures.

Modular Liquid Cooling: A Smarter Approach

To address these challenges, modular liquid-cooled architectures provide a more effective and scalable solution. Rather than relying solely on flat cold plates, this approach integrates cooling directly into the structure of the power conversion system. Coolant flows around the electronics, dramatically shortening thermal paths and allowing components to be more directly coupled to the cooling structure.

This design improves heat extraction across all components, not just the highest power devices, while also reducing internal temperature gradients throughout the system. The result is higher power density, improved thermal performance, and greater overall reliability. In addition, modular architectures support scalability and simplify electromagnetic interference (EMI) design by allowing better partitioning of system elements.

By combining performance, manufacturability, and reliability, modular liquid cooling represents a significant advancement over traditional approaches.

Next-Level Innovation: Direct Immersion Cooling

An even more advanced solution involves direct immersion cooling, where electronic assemblies are fully encapsulated in a dielectric fluid such as oil. In this approach, the fluid acts as both an electrical insulator and a highly effective thermal medium, directly absorbing and transferring heat away from components. The heated fluid is then circulated through the system to dissipate energy efficiently.

This method provides a near-isothermal environment, meaning temperatures across components remain more uniform. It also delivers exceptional environmental protection by sealing electronics from dust, moisture, and other contaminants, while simultaneously reducing the impact of shock and vibration. Another key advantage is that existing air-cooled designs can often be adapted with minimal redesign, making this approach both innovative and practical.

In some cases, a variety of fluids may be used, including transformer oil, mineral oil, or even diesel fuel, offering potential logistical advantages in military applications where fuel is already readily available.

Why Temperature Matters: Reliability Explained

The relationship between temperature and reliability in electronic systems is well understood and often modeled using the Arrhenius equation:

R(t)=Ae−EAkTR(t) = A e^{-\frac{E_A}{kT}}R(t)=Ae−kTEA​​

This model demonstrates that failure rates increase exponentially as temperature rises. A widely accepted rule of thumb is that for every 10°C increase in temperature, component failure rates can increase by a factor of two to eight.

In practical terms, traditional liquid-cooled systems may still see component temperatures reaching 100°C (212°F) or higher, whereas immersion-cooled systems can reduce operating temperatures to approximately 70°C (158°F). This 30°C reduction can result in up to a 100× improvement in reliability,  making thermal management one of the most critical factors in system design.

Conclusion: Cooling Is Now a Strategic Design Lever

As military vehicles continue to evolve toward hybrid-electric architectures and higher power demands, power conversion systems must advance accordingly. High-voltage systems enable greater efficiency and scalability, but they also introduce new thermal challenges that must be addressed through innovative design.

Harsh operating environments demand sealed, ruggedized solutions, and traditional air cooling methods are often insufficient. While liquid cooling is essential, its implementation must go beyond conventional approaches to fully address internal temperature rise and system reliability. Modular and immersion-based cooling technologies offer the most effective path forward.

Ultimately, thermal management is no longer just a design constraint; it is a strategic advantage that directly impacts performance, reliability, and mission success.

Want to Learn More?

If you're designing power systems for military vehicles, radar and communications platforms, or hybrid-electric systems, understanding cooling architecture is critical. The right approach can mean the difference between operational success and system failure in the field.